The sides of a triangle are:

a = 12 cm., b = 10 cm, c = 8 cm

What is the sum of the 3 heights each perpendicular to the 3 sides ?

The answer is 24.27. I think I can solve it if I understood the problem. But I can't, I am from a non-English speaking country. Maybe struggling with how the sentence was constructed. Could someone help me out ?